| Summary: | We fabricated Al/Al<sub>2</sub>O<sub>3</sub>/SiO<sub>2</sub>/Si and Al/HfO<sub>2</sub>/Si structures to optimize the passivation layer of a backside-illuminated (BSI) complementary metal oxide semiconductor (CMOS) image sensor (CIS), with the key properties of the newly developed high-<inline-formula> <tex-math notation="LaTeX">$k$ </tex-math></inline-formula> passivation layer analyzed via border traps, interface traps, and fixed charges. In the first experiment using Al<sub>2</sub>O<sub>3</sub>/SiO<sub>2</sub> bilayer-based structures, different thicknesses of SiO<sub>2</sub> were applied from 0 to 15 nm. The improvement in their properties was confirmed by applying forming gas annealing (FGA), a type of post-treatment, to all experimental systems. The first experiment results indicated that both the SiO<sub>2</sub> layer and FGA were effective for chemical passivation. However, a tradeoff occurred in the degree of improvement of the interface trap density (<inline-formula> <tex-math notation="LaTeX">$\text{D}_{\mathrm {it}}$ </tex-math></inline-formula>) and fixed-charge density (<inline-formula> <tex-math notation="LaTeX">$\text{Q}_{\mathrm {f}}$ </tex-math></inline-formula>) according to the SiO<sub>2</sub> layer thickness. Subsequently, in the second experiment using HfO<sub>2</sub> single-layer-based structures, FGA improved the border trap to a relatively poor extent compared to the first experiment. Nevertheless, FGA improved the electrical characteristics of the HfO<sub>2</sub> films without any side effects and results in optimal <inline-formula> <tex-math notation="LaTeX">$\text{D}_{\mathrm {it}}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$\vert \text{Q}_{\mathrm {f}}/\text{q}\vert $ </tex-math></inline-formula> values of <inline-formula> <tex-math notation="LaTeX">$2.59 \times 10^{11}$ </tex-math></inline-formula> eV<inline-formula> <tex-math notation="LaTeX">$^{-1}$ </tex-math></inline-formula> cm<inline-formula> <tex-math notation="LaTeX">$^{-2}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$1.00 \times 10^{12}$ </tex-math></inline-formula> cm<inline-formula> <tex-math notation="LaTeX">$^{-2}$ </tex-math></inline-formula>, respectively, demonstrating its potential for the passivation layer in BSI CIS applications.
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